The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with dis-closures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
Scheduling refers to a process of dividing and allocating resources between user terminals that have data to transfer or receive. In LTE, dynamic scheduling (with a minimum time granularity of 1 ms) is applied both to the uplink and downlink. Scheduling should result in a balance between perceived end-user quality and overall system performance.
For services with small payloads and regular packet arrivals, the control signalling required for dynamic scheduling might be disproportionately large relative to the amount of user data transmitted. For this reason, LTE also supports persistent scheduling (in addition to dynamic scheduling). Persistent scheduling implies that radio resources are allocated to a user for a given set of sub-frames.
Thus, user terminals may be scheduled on the LTE air interface by using dynamic scheduling. Scheduling may be fully dynamic. In downlink direction resources may be assigned when data is available. For data to be sent in the uplink, the user terminal dynamically requests transmission opportunities when data arrives in the user terminal's uplink buffer. Scheduling information related to data being sent in downlink direction or uplink transmission resources are carried in a physical downlink control channel (PDCCH) which is available at the beginning of each downlink sub-frame. User terminals may also be scheduled on the LTE air interface by using semi-persistent scheduling (SPS). While dynamic scheduling is suited for bursty, infrequent and bandwidth consuming data transmissions (e.g. web surfing, video streaming, emails) it is less suited for deterministic low data rate applications, such as voice calls. If the data rate of the stream is very low, as is the case for voice calls, the overhead of the scheduling messages is very high as only little data is sent for each scheduling message. The solution for this is semi-persistent scheduling. Instead of scheduling each uplink or downlink transmission separately, a transmission pattern is defined instead of single opportunities. This significantly reduces the scheduling assignment overhead.
During silent periods, the wireless voice codecs may stop transmitting voice data and may only send silence description information with much longer time intervals in between. Only retransmissions and SID frames are scheduled dynamically, i.e. it may be referred to as semi-persistent scheduling.